The avian sebaceous gland contains undifferentiated basal cells and differentiated sebocytes. The small basal cells are almost completely filled with their nuclei. These cells lie on a basement membrane and contain none of the wax ester secretion product of the gland and little or none of the enzymes required to synthesize the wax ester. Mature sebocytes are large and filled with the wax ester secretion product. The entire mature sebocyte with its contents is secreted from the gland. Continual proliferation of the basal cells gives rise to more progenitor cells and to immature sebocytes which replace those lost by secretion. As the progenitor cells detach from the basement membrane and acquire the characteristics of mature sebocytes, they accumulate malic enzyme and fatty acid synthase, two enzymes involved in the de novo synthesis of the wax ester secretion product. We propose to determine the molecular nature of the events which initiate conversion of progenitor cells to sebocytes, using malic enzyme and fatty acid synthase as markers of the differentiated state. Enzyme synthesis seems to regulate the level of these enzymes in the avian sebaceous gland. We will confirm this and then determine whether enzyme synthesis is regulated at the level of transcription, processing or translation of the specific mRNAs. We have isolated cloned cDNA probes for malic enzymes and fatty acid synthase mRNAs. They will be used to measure mRNA levels and rates of transcription in isolated progenitor cells and sebocytes and to analyze the structure of the malic enzyme and fatty acid synthase genes in the gland. Progenitor cells will be established in primary culture to test various possible mechanisms which might initiate the differentiation process.